The present invention relates to an apparatus for multiplexing between on-board units of a vehicle by using wire harnesses.
Recently, various controls in a vehicle are performed by an on-board computer and the associated electrically controlled equipments. Thus, large amounts of electric wiring are used in the vehicle. The electric wiring, such as the wire harnesses, have the potential for causing a short-circuit. Therefor, various apparatus for detecting the short-circuit of wire harnesses for power supply have been proposed in the past.
One of them is disclosed in Japanese Patent publication No. 4-17809 (1992), in which the rated consumption currents for respective loads are calculated in advance, the occurrence of an abnormality due to the short-circuit is detected by comparing the sum of the rated consumption currents with the sum of the current one in the vehicle.
However, when a wire harness is installed into a vehicle body, the harness may be jammed into the vehicle body and/or the coating of the harness may be broken due to the rubbing of the harness on metal portions of the vehicle body. Therefore, a core wire of an electric power source may short to a ground portion of the vehicle body, and thus serious accidents such as a fire in the vehicle may break out in the worst case.
In the above prior art, the apparatus is constructed such that the serious accidents can be prevented immediately by cutting off the whole current. Therefore, when such accidents occur during driving, a power source is cut off. As a result, the vehicle stops suddenly. Further, when the driver changes the load of an electric system, it is required to change the predetermined rated value. Therefore, there was a possibility that a malfunction would occur. In addition, while the short-circuit of the wire harness can be detected, the processing after the detection of the short-circuit can not be performed.